What is a Stormwater Management Pond?

There are a number of storm water ponds throughout the City, in residential areas the main sites are two in the Heritage Park subdivision, Twin Lakes, Blackwell Glen, and by the Suncor Nature Trail. A stormwater management pond (SWMP) is an artificial pond that is designed to collect and retain urban stormwater. They are frequently built into urban areas in North America to also retain sediments and other materials. A (SWMP) is an engineered structure constructed to gather rainfall and surface water runoff. The pond temporarily stores water and then releases it at a controlled rate. A single pond can provide erosion and flooding control while enhancing water quality. In urban areas, impervious surfaces (roofs, roads) reduce the time spent by rainfall before entering into the stormwater drainage system. If left unchecked, there is potential to cause widespread flooding downstream. The function of a stormwater pond is to contain this surge and release it slowly. This slow release mitigates the size and intensity of storm-induced flooding on downstream receiving waters. Stormwater ponds also collect suspended sediments, which are often found in high concentrations in stormwater water due to upstream construction and sand applications to roadways

Through a combination of landscape and structural features, stormwater management ponds allow sediment and contaminants to settle out of runoff before it is released into a natural watercourse. Stormwater ponds also hold back water in order to release it at a controlled rate during large storms. Controlling the flow of stormwater protects downstream lands from erosion and flooding.

In addition, stormwater ponds are constructed to be an attractive feature with an environmental benefit. Stormwater management facilities are designed to be surrounded by natural vegetation and to provide habitat for birds and animals.

How Can You Help? 

Protect Natural Buffers

Stormwater ponds are designed to mimic a natural system; therefore, it is important to allow a natural buffer to grow around the perimeter of the pond. The natural buffer is made up of native plants and grasses and should not be mown or trimmed. It is important to note that the property lines for homes near stormwater ponds do not extend to the water’s edge. These buffer areas should not be mown or altered.

Reduce or eliminate the use of Pesticides and Fertilizers

The use of pesticides or fertilizers in grassed lawns around stormwater ponds should be limited or eliminated completely. These chemicals are easily carried away by runoff into the stormwater pond which can cause algae blooms and negative impacts to the downstream natural watercourse. Where possible, use organic alternatives to chemicals and plant native species that require low maintenance and no pesticides.

Plant Wisely

Planting native species of trees, shrubs, grasses and flowers has numerous benefits. These species can dramatically reduce the amount of water used for irrigation, chemicals used for pest control, and fertilizers used for growth. Information on native landscaping species can be obtained from the Saint Clair Conservation Authority.

 Managing Yard Waste

Dumped yard waste in natural areas or around stormwater ponds can have adverse effects on the health of the natural system. Dumped materials smother natural vegetation, may contain harmful chemicals, and non-native plant seeds.  The best solution is to compost leaves, grass clippings, and weeds on your own property. The City of Sarnia has yard waste collection days for brush and leaves throughout the year. To learn more about waste collection days, please refer to the most recent version of the City of Sarnia’s Collection Calendar.

What is algae?

Is it bad? A common misconception is that the presence of algae represents an unhealthy detention pond. This isn’t true! When you see green murky water, that is nature’s way of responding to a load of nutrients that have washed into the pond. This produces an increase in the plankton algae population, which in response provides oxygen and food for other aquatic animals. Their growth and reproduction is directly proportional to the amount of nutrients in the water, therefore many stormwater ponds have an abundance of algae as a result of the runoff from residential and commercial development. However, there is such a thing as too much algae.

A severe algae bloom can cause a fish kill because the death and decay of the algae will remove oxygen from the water. Everything in moderation! Is there any “bad” algae? Absolutely! One group of algae, known as blue-green algae (cyanobacteria) can produce toxins that can affect the health of fish and animals that come in contact with the water. Usually this type of algae occurs when a pond receives an excessive amount of phosphorus or animal waste.

The benefits of algae!

  • Algae in pond water makes a great natural and healthy food for fish. Often times, algae is a better form of nutrition than some products sold in stores!
  • One of the biggest benefits of algae is that it produces oxygen in the water. Algae in ponds is natural way to keep sufficient oxygen levels for the aquatic life.
  • Did you know that certain types of algae promote the presence of good bacteria? The algae serves as a home for the bacteria, which in turn provides a healthy pond.

Is murky green water unhealthy? Should the water be clear?

No, not necessarily. The murkiness is a sign of a growing plankton population which is responding to nutrients that have washed into the pond. This is Nature’s way of capturing nutrients that might otherwise contaminate rivers and beaches. The image below shows a healthy pond where green algae are managing nutrients in the water.

Are there any particularly bad algae? 

Yes. One group of algae, known as blue-green algae (cyanobacteria), can produce toxins that can affect the health of fish and animals that come into contact with the water. Cyanobacteria often becomes a problem when the pond receives too much phosphorous, a condition that is most often associated with runoff that contains excessive lawn fertilizers or animal wastes. Cyanobacteria are normally very bright green and usually form a film on the surface. Most other planktonic algae are darker green and do not form surface films. There are some cyanobacteria that do not form surface films and a few that are filamentous. On occasion, a pond may develop algae which also may be harmful to aquatic animals. “Red algae” is not actually algae, but its growth and control are similar to that of other planktonic algae.

Prevention and Control

Algae are able to thrive only when they have enough food sunlight and nutrients to grow, so reducing either the amount of light or nutrients is the key. Since the sun comes up every day, we are limited in ways to reduce sunlight. For a long term solution to reduce algae, the nutrients in the pond need to be addressed. Sweep or blow fertilizer off the roads to prevent from washing down the storm drain. Decrease or eliminate use of fertilizers on the banks of slopes and landscaping. Properly dispose of grass clippings and yard waste. Pick up your pet waste! Plant wetland plants along the shoreline to filter runoff and absorb nutrients. Encourage underwater vegetation in the pond to extract nutrients directly from the water.